| 1. |
- Alerstam, Thomas, et al.
(författare)
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Convergent patterns of long-distance nocturnal migration in noctuid moths and passerine birds.
- 2011
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Ingår i: Royal Society of London. Proceedings B. Biological Sciences. - : The Royal Society. - 1471-2954. ; 278, s. 3074-3080
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Tidskriftsartikel (refereegranskat)abstract
- Vast numbers of insects and passerines achieve long-distance migrations between summer and winter locations by undertaking high-altitude nocturnal flights. Insects such as noctuid moths fly relatively slowly in relation to the surrounding air, with airspeeds approximately one-third of that of passerines. Thus, it has been widely assumed that windborne insect migrants will have comparatively little control over their migration speed and direction compared with migrant birds. We used radar to carry out the first comparative analyses of the flight behaviour and migratory strategies of insects and birds under nearly equivalent natural conditions. Contrary to expectations, noctuid moths attained almost identical ground speeds and travel directions compared with passerines, despite their very different flight powers and sensory capacities. Moths achieved fast travel speeds in seasonally appropriate migration directions by exploiting favourably directed winds and selecting flight altitudes that coincided with the fastest air streams. By contrast, passerines were less selective of wind conditions, relying on self-powered flight in their seasonally preferred direction, often with little or no tailwind assistance. Our results demonstrate that noctuid moths and passerines show contrasting risk-prone and risk-averse migratory strategies in relation to wind. Comparative studies of the flight behaviours of distantly related taxa are critically important for understanding the evolution of animal migration strategies.
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| 2. |
- Alerstam, Thomas
(författare)
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Optimal bird migration revisited
- 2011
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Ingår i: Journal of Ornithology. - : Springer Science and Business Media LLC. - 2193-7206 .- 2193-7192. ; 152, s. 5-23
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Forskningsöversikt (refereegranskat)abstract
- Using optimality perspectives is now regarded as an essential way of analysing and understanding adaptations and behavioural strategies in bird migration. Optimization analyses in bird migration research have diversified greatly during the two recent decades with respect to methods used as well as to topics addressed. Methods range from simple analytical and geometric models to more complex modeling by stochastic dynamic programming, annual routine models and multiobjective optimization. Also, game theory and simulation by selection algorithms have been used. A wide range of aspects of bird migration have been analyzed including flight, fuel deposition, predation risk, stopover site use, transition to breeding, routes and detours, daily timing, fly-and-forage migration, wind selectivity and wind drift, phenotypic flexibility, arrival time and annual molt and migration schedules. Optimization analyses have proven to be particularly important for defining problems and specifying questions and predictions about the consequences of minimization of energy, time and predation risk in bird migration. Optimization analyses will probably also be important in the future, when predictions about bird migration strategies can be tested by much new data obtained by modern tracking techniques and when the importance of new trade-offs, associated with, e.g., digestive physiology, metabolism, immunocompetence and disease, need to be assessed in bird migration research.
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| 3. |
- Boström, Jannika, et al.
(författare)
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Where on earth can animals use a geomagnetic bi-coordinate map for navigation?
- 2012
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Ingår i: Ecography. - : Wiley. - 1600-0587 .- 0906-7590. ; 35:11, s. 1039-1047
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Tidskriftsartikel (refereegranskat)abstract
- Many animal taxa have been shown to possess the ability of true navigation. In this study we investigated the possibilities for geomagnetic bi-coordinate map navigation in different regions of the earth by analysing angular differences between isolines of geomagnetic total intensity and inclination. In no-grid zones where isolines were running almost parallel, efficient geomagnetic bi-coordinate navigation would probably not be feasible. These zones formed four distinct areas with a north-south extension in the northern hemisphere, whereas the pattern in the southern hemisphere was more diffuse. On each side of these zones there was often a mirror effect where identical combinations of the geomagnetic parameters appeared. This may potentially cause problems for species migrating long distances east-west across longitudes, since they may pass areas with identical geomagnetic coordinates. Migration routes assumed for four populations of migratory passerine birds were used to illustrate the possibilities of geomagnetic bi-coordinate map navigation along different routes. We conclude that it is unlikely that animal navigation is universally based on a geomagnetic bi-coordinate map mechanism only, and we predict that the relative importance of geomagnetic coordinate information differs between animals, areas and routes, depending on the different conditions for bi-coordinate geomagnetic navigation in different regions of the earth.
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| 4. |
- Chapman, Jason W., et al.
(författare)
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Animal Orientation Strategies for Movement in Flows
- 2011
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Ingår i: Current Biology. - : Elsevier BV. - 1879-0445 .- 0960-9822. ; 21:20, s. 861-870
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Forskningsöversikt (refereegranskat)abstract
- For organisms that fly or swim, movement results from the combined effects of the moving medium - air or water - and the organism's own locomotion. For larger organisms, propulsion contributes significantly to progress but the flow usually still provides significant opposition or assistance, or produces lateral displacement ('drift'). Animals show a range of responses to flows, depending on the direction of the flow relative to their preferred direction, the speed of the flow relative to their own self-propelled speed, the incidence of flows in different directions and the proportion of the journey remaining. We here present a classification of responses based on the direction of the resulting movement relative to flow and preferred direction, which is applicable to a range of taxa and environments. The responses adopted in particular circumstances are related to the organisms' locomotory and sensory capacities and the environmental cues available. Advances in biologging technologies and particle tracking models are now providing a wealth of data, which often demonstrate a striking level of convergence in the strategies that very different animals living in very different environments employ when moving in a flow.
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| 5. |
- Grönroos, Johanna, et al.
(författare)
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Fine-scaled orientation changes in migrating shorebirds
- 2012
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Ingår i: Ardea. - : Netherlands Ornithologists' Union. - 0373-2266. ; 100:1, s. 45-53
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Tidskriftsartikel (refereegranskat)abstract
- Flight directions and routes of migrating birds are determined by the birds' compass orientation, but also by effects of wind, social influence, responses to topography and landmarks, and to navigation cues. We investigated the orientation and routes taken by arctic shorebirds during autumn migration in southern Sweden at three different sites situated within a distance of 200 km from each other, in relation to the birds' destinations. We used three different methods, visual telescope observations, tracking radar registration and ring recoveries. Mean track directions differed significantly between the different sites in a way that demonstrated fine-scaled orientation changes when the shorebirds passed the southern Baltic region. The gradual change cannot be explained by different wind conditions at the different sites or by distinct responses to specific topographical features, i.e. the birds were not following coastlines or prominent landmarks in any detailed way. Neither could it be reconciled with orientation according to any of the main compass mechanisms known to be used by migrating birds which indicates that the control of flight courses and paths may be more complex than expected. The shorebirds might travel within a slightly winding flight corridor in broad agreement with the large-scale topography to maximize general association with coastal habitats during migration. Juvenile birds had a significantly different orientation than adults, particularly when the juveniles travelled in flocks without any adults. Juvenile birds may learn the general flight paths and course changes in relation to the large-scale topography from older and experienced individuals in the flocks, but most of this learning process between generations probably does not take place until after the birds' first autumn migration.
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| 6. |
- Grönroos, Johanna, et al.
(författare)
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Orientation of shorebirds in relation to wind: both drift and compensation in the same region
- 2013
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Ingår i: Journal of Ornithology. - : Springer Science and Business Media LLC. - 2193-7206 .- 2193-7192. ; 154:2, s. 385-392
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Tidskriftsartikel (refereegranskat)abstract
- Migratory movements in air or water are strongly affected by wind and ocean currents and an animal which does not compensate for lateral flow will be drifted from its intended direction of movement. We investigated whether arctic shorebirds during autumn migration in the region of South Sweden and the southern Baltic Sea compensate for wind drift or allow themselves to be drifted when approaching a known goal area under different circumstances (over sea, over land, at low and high altitude) using two different approaches, visual telescope observations and tracking radar. The shorebirds showed clearly different responses to crosswinds along this short section (<200 km) of the migratory journey, from almost full drift when departing over the sea, followed by partial drift and almost full compensation at higher altitudes over land during later stages. Our study demonstrates that shorebirds are also remarkably variable in their response to crosswinds during short sections of their migratory journey. The recorded initial drift close to departure is probably not adaptive but rather a result of constraints in the capacity of the birds to compensate in some situations, e. g. in low-altitude climbing flight over the sea. We found no difference in orientation response to wind between adult and juvenile birds. This study indicates, in addition to adaptive orientation responses to wind, the importance of the non-adaptive wind drift that contributes to increasing the variability of drift/compensation behaviour between places that are separated by only short distances, depending on the local topographic and environmental conditions.
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| 7. |
- Grönroos, Johanna, et al.
(författare)
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To fly or not to fly depending on winds: shorebird migration in different seasonal wind regimes
- 2012
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Ingår i: Animal Behaviour. - : Elsevier BV. - 1095-8282 .- 0003-3472. ; 83:6, s. 1449-1457
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Tidskriftsartikel (refereegranskat)abstract
- Migratory birds are predicted to adapt their departure to wind, changing their threshold of departure and selectivity of the most favourable winds in relation to the mean, scatter and skewness of the wind regime. The optimal departure behaviour depends also on the importance of time and energy minimization during migration and on the ratio of cost of flight to cost of resting and waiting for more favourable winds. We compared departure and flight activity of shorebirds migrating in contrasting wind regimes during autumn (high probability of wind resistance) and spring (high probability of wind assistance) in southern Scandinavia, using data obtained by radiotelemetry, radar tracking and visual observations. The shorebirds changed their threshold for departure in relation to wind between the two seasons, flying almost exclusively with wind assistance in spring but regularly with wind resistance during autumn. The degree of wind selectivity in relation to the distributions of available wind effects was similar during autumn and spring indicating that reducing time and energy costs for migration was important during both seasons. These results demonstrate that migratory birds change departure behaviour in relation to the prevailing wind regime. It remains unknown whether they change behaviour not only seasonally but also in different zones along the migration route and whether they respond to differences not only in mean wind conditions but also in scatter and skewness between wind regimes. Our study indicates the possible existence of an adaptive flexibility in responses to wind regimes among migratory birds. (c) 2012 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
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| 8. |
- Karlsson, Håkan, et al.
(författare)
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Compensation for wind drift by migrating swifts
- 2010
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Ingår i: Animal Behaviour. - : Elsevier BV. - 1095-8282 .- 0003-3472. ; 80:3, s. 399-404
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the orientation in relation to wind of common swifts, Apus apus, during nocturnal spring and autumn migration. Swifts are highly adapted to a life in the air, showing wind-dependent orientation during nocturnal roosting flights, and may be expected to be more efficient in their wind drift/compensation behaviour than nocturnal passerine migrants, which are usually subjected to full or partial wind drift. A tracking radar at Lund in southern Sweden was used to record the orientation of common swifts (identified by their characteristic radar echo signature) on nocturnal migration flights and to measure wind conditions at the altitudes at which the birds were flying. Comparing track and heading directions under easterly and westerly winds revealed that the swifts shifted their heading distinctly into the wind, with the result that track directions were similar under the different wind conditions. As this pattern of complete compensation for drift from cross-winds occurred during both spring and autumn migration, there were no indications of differences between age classes. In addition, we found an effect of side-winds on equivalent airspeeds, with swifts increasing their airspeed with increasing wind speed. Such a response has been theoretically predicted as part of an optimal behaviour for counteracting wind drift but has hereto not been empirically demonstrated. There was also a positive correlation between overall wind speed and equivalent airspeed, making it difficult to interpret whether the swifts respond to the total wind speed rather than specifically to the side-wind effect. Our results suggest that important differences may exist between species in their capacities to orient in relation to the wind and that the swift may be particularly efficient in adjusting heading direction and airspeed to obtain complete compensation for wind drift during high-altitude nocturnal migratory flights. (C) 2010 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
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| 9. |
- Karlsson, Håkan, et al.
(författare)
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Exaggerated orientation scatter of nocturnal passerine migrants close to breeding grounds: comparisons between seasons and latitudes
- 2010
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Ingår i: Behavioral Ecology and Sociobiology. - : Springer Science and Business Media LLC. - 1432-0762 .- 0340-5443. ; 64:12, s. 2021-2031
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Tidskriftsartikel (refereegranskat)abstract
- Using tracking radars, we investigated the variability of flight directions of long-distance nocturnal passerine migrants across seasons (spring versus autumn migration) and sites at the southern (56A degrees N) and northern (68A degrees N) ends of the Scandinavian Peninsula (Lund versus Abisko). Whilst most migrants at Lund are on passage to and from breeding sites in Fennoscandia, the majority of the migrants at Abisko are close to their breeding sites, and migration at Abisko thus to a large degree reflects initial departure from breeding sites (autumn) or final approach to breeding destinations (spring). The radar data were used to test predictions about differences in orientation and wind drift effects between adult and juvenile birds (a large proportion of autumn migrants consists of juvenile birds on their first journey), between situations far away from or near the goals and between different phases of migration (initial departure, en route passage, final approach to goal). The concentrations (both total and within-night concentrations) of flight directions differed significantly between seasons as well as sites, with the highest concentration at Lund in spring (mean vector length of track directions, r = 0.79) and lowest at Abisko during spring (r = 0.35). Partial wind drift and partial compensation were recorded at Lund, with a similar effect size in spring and autumn, whilst possible wind drift effects at Abisko were obscured by the large directional scatter at this site. The results from Lund support the prediction that the high proportion of juveniles in autumn contributes to increase the directional scatter during this season, whilst there was no support for predictions of differential wind drift effects between seasons and situations with different goal distances. The most striking and surprising result was the exceedingly large scatter of flight directions at Abisko, particularly in spring. We suggest that such an exaggerated scatter may be associated with final approach orientation, where migrants reach their specific goals from all various directions by final navigation within a more wide-ranging goal region. The larger scatter of autumn flight directions at Abisko compared to Lund may be due to exploratory flights in variable directions being more common at initial departure from breeding sites than later during migratory passage. These surprising results highlight the importance of studying and analysing orientation during final approach to (and initial departure from) migratory goals for understanding the orientation systems of migratory birds.
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| 10. |
- Karlsson, Håkan, et al.
(författare)
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Nocturnal passerine migrants fly faster in spring than in autumn: a test of the time minimization hypothesis
- 2012
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Ingår i: Animal Behaviour. - : Elsevier BV. - 1095-8282 .- 0003-3472. ; 83:1, s. 87-93
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Tidskriftsartikel (refereegranskat)abstract
- It has been suggested that time selection and precedence in arrival order are more important during spring than autumn migration. Migrating birds are expected to fly at faster airspeeds if they minimize duration rather than energy costs of migration, and they are furthermore expected to complete their journeys by final sprint flights if it is particularly important to arrive at the destination before competitors. We tested these hypotheses by tracking-radar studies of nocturnal passerine migrants during several spring and autumn seasons at Lund (56 degrees N) and Abisko (68 degrees N) at the southern and northern ends of the Scandinavian Peninsula, respectively. The samples from these two sites represent migrants that are mostly rather far from (Lund) or close to (Abisko) their breeding destinations. We found that the birds were flying at clearly faster airspeeds in spring than in autumn at both study sites, with spring speeds exceeding autumn speeds by, on average, 16%, after taking effects of wind conditions and vertical flight speeds into account. This difference in speeds could not be explained by seasonal differences in body mass or wing morphology and thus supports the hypothesis of time-selected spring migration. There was also a significantly larger seasonal difference in airspeed at Abisko than at Lund, suggesting that the birds may have shown an inclination to sprint on their final spring flights to the breeding destinations, although this possible extra sprint effort was modest. (C) 2011 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
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